German Patent No. DE 44 47 005 describes a device for determining a rotational speed, with a sensor being set in a constant state of excitation by a starter loop. Furthermore, the device has a detector loop for detecting a motion parameter and an analyzer loop for generating an output voltage proportional to the rotational speed. An external scaling factor defined as the ratio of the output voltage generated to the rotational speed to be measured is subject to changes over time, because the sensitivity of the sensor can change with temperature or with increasing age.